Notes on the Spread of Novel Coronavirus

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Here are some important new developments on the novel Coronavirus over the last 24 hours.

As you’ve probably seen, there’s been an uptick of new cases, mostly but not only on the West Coast of the US, which appear to be from community spread – basically transmission in the wild, as it were, that can no longer be tracked by public health officials who try to reconstruct the specific chain of transmission. There are cases in California, Oregon, Washington state, Chicago and apparently Rhode Island.

A key development last night comes out of Washington state where epidemiologists analyzed the genome of a new community spread case and compared it to an already known case discovered roughly six weeks ago (January 19th). That analysis strongly suggested, though it didn’t yet prove, that both infections were parts of a common stream of transmission. In other words, this new evidence strongly suggests that community transmission has been taking place in Washington state since late January.

Here’s the Twitter thread from Trevor Bedford, an Associate Professor at the University of Washington and investigator at the Fred Hutch research institute in the state. (I’ve confirmed Bedford’s credentials and his report has been confirmed and reported in respected news outlets.)

All of this suggests that community spread, though likely as yet quite limited, has been in process in the United States for some time but has not been confirmed because testing was only taking place for a very limited category of people.


The answer seems to be problems with the initial version of the test. Since there weren’t enough tests to go around the CDC restricted their use to a very small spectrum of people – basically people who were symptomatic with recent travel histories to China or who had close contact with travelers.

With not enough tests to go around that decision makes good sense. But it also seems clear there was a gap in communication with the public. The public message, at least as I was hearing it, was not ‘we can only do a limited number of tests for now’ but ‘these are the only people who need to be tested.’

How much this slowed down efforts to slow the spread of the virus I’m not qualified to answer.

I will say this. The CDC is now rapidly expanding the categories of people who are going to be tested and they appear to have a lot of test capacity coming online. That means we should expect a fairly rapid rise in the number of active cases. By rapid in this case I would figure from the dozens into the hundreds. But it’s important to remember that this surge will mainly or partly be finding out about spread that was happening, without formal detection over recent weeks, rather than an actual surge of infections over the next number of days.

Here are some interesting and helpful articles.

Key terms of the coronavirus outbreak, explained: From asymptomatic to zoonotic

How Does the Coronavirus Compare With the Flu?

A critical question in getting a handle on coronavirus: What role do kids play in spreading it?

COVID-19—New Insights on a Rapidly Changing Epidemic (JAMA, Feb. 28)

Why Some COVID-19 Cases Are Worse than Others

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